Composition Suitable for Single-Sided, Low-Noise, Stretch Cling Film and Films Made Therefrom

ABSTRACT

The invention is directed to a composition suitable for use in a single-sided stretch cling film, the composition having from 0.1 to 20 percent by weight of a propylene-based copolymer having substantially isotactic propylene sequences, and having from 80 to 99 percent by weight of an ethylene-based copolymer having a density of at least 0.905 g/cc, wherein a film made from the composition exhibits cling layer to release layer cling of at least 70 grams force per inch as measured by ASTM D-5458-95, noise levels of less than 87 dB during unwinding operations, and has a modulus of at least 3 MPA as determined by ASTM D-882.

FIELD

This invention pertains to thermoplastic compositions suitable for usein the manufacture of single-sided, stretch cling film exhibitinglow-noise characteristics. More particularly, the invention pertains topolyolefin blends that can be used to manufacture low-noise, stretchcling films without the need of functional polymers or low molecularweight tackifiers. Additionally, the invention pertains to multilayerfilms incorporating the inventive composition in a cling layer of thefilm.

BACKGROUND

Single-sided stretch cling films are used by the packaging industry toover-wrap packages of goods, particularly they have been used tosecurely hold and/or wrap an article or group of articles, such as theuse of an over-wrap film for the unitization of a pallet full of goods.In these applications, the films ideally should have high strength, beresistant to tear and puncture, and exhibit single-sided clingproperties. The single-sided cling properties are important to preventindividual pallets' over-wrap from clinging to each other, which couldresult in tearing and/or destruction of the over-wrap and, ultimately,separation of goods from the pallet.

Generally, single-sided cling film is comprised of a cling layer and arelease layer. The release layer does not have to have non-clingcharacteristics, but it does typically exhibit lower clingcharacteristics than the cling layer. The cling film is typicallyco-extruded with an A/B film layer structure. The cling layer typicallycomprises the A layer while the release layer typically comprises the Blayer. In general, the cling force measured between two A layers ofadjacent film structures and between the A layer of one film and the Blayer of another film, is much greater than the cling force exhibitedbetween the B layer of one film and the B layer of an adjacent film.Sometimes a third layer, C, is added to form an A/C/B film structure. Inthis type of film, the B is again the release layer and the C layer is acore layer that is used to obtain specific properties in the cling filmand can consist of more than one physical layer. For example, if ahigher modulus film is desirable, then the C layer may comprise apolymer that exhibits a higher modulus compared to the A or B layers.

Typically, the single-sided stretch cling film is wrapped around thegoods to be unitized (such as cases of goods loaded on or to be loadedon a pallet), either using a hand applicator or a semi- or totallyautomated machine, in such a manner that a cling layer is laying overand adjacent to release layer of film. In most typical applications, thefilm needs to be stretched as it is applied to the goods in order todevelop sufficient holding force for maintaining the integrity of thegoods (such as a pallet of goods) to be unitized. This typicallyrequires the single-sided stretch cling film to be capable of beingstretched to 100%, often 200%, of its original length, while stillmaintaining its mechanical integrity and exhibiting adequate cling forcebetween the cling layers and release layers where they contact.

In order to provide film structures providing adequate holding force,ethylene homopolymers and ethylene-based copolymers have been utilized(both hereinafter sometimes referred to as “polyethylene(s)).Polyethylene, having densities greater than 0.915 g/cc, provide adequateholding force, but they do not provide sufficient cling force for mostapplications. Therefore, the single-sided stretch cling films utilizinglower density polyethylene for the cling layer and higher density forthe release layer have been developed. Unfortunately, for a film of agiven overall thickness, a film using a lower density polyethylene inthe cling layer and a higher density polyethylene in the release layeroften has substantially lower holding force than a film made of just thehigher density polyethylene. This will require a cling film having alarger thickness than desirable. Additionally, very low densitypolyethylene (having densities between 0.880 g/cc and 0.914 g/cc) aretypically necessary to obtain the desired cling properties.

Single-sided stretch cling resins utilizing a polyethylene ofsufficiently low density to provide adequate cling properties, oftengenerate considerable noise as they are unwound from their supply rollin the process of wrapping the goods. In some cases, such as whereextremely low density polyethylene is utilized, the noise generated maybe in excess of that which can be safely tolerated for long-termexposure by the human ear. This is particularly problematic when thefilm is to be unwound by hand or using a semi-automated machine, becauseof the presence of personnel close to the supply roll.

As an alternative to films using very low density polyethylene for thecling layer, single-sided stretch cling films have been developed whichutilize minor amounts of low molecular weight tackifiers. Commontackifiers include polybutylenes, mono- and diglycerides of fatty acids,low molecular weight amorphous polypropylenes, terpene resins and rosinesters.

These tackifiers tend to be migratory within the film and can causedie-lip build-up during film fabrication, and other undesirableaccumulations on equipment during wrapping operations, that necessitateperiodic stoppage of operations for cleaning and maintenance. Moreover,since they are migratory, they often migrate to adjacent and other filmslayers (and into the release layer of an adjacent film), thereby causingundesired adhesion and dirt retention problems commonly associated withtwo-sided cling film structures. Also, if the tackifiers migrate to therelease layer of the film, it may result in one unitized pallet of goodsto cling or drag against an adjacent unitized pallet thereby causingtransportation and handling problems. Because of the cling natureimparted to the over-wrap by the migrated tackifier, one suchover-wrapped pallet of goods may not readily slide against an adjacentpallet of goods. The tendency is for the over-wrap of one pallet to pulldestructively upon the over-wrap of an adjacent pallet because of thecling nature imparted by migrated tackifier. This can be a problem inwholesale and retail goods distribution centers where pallets of goodsare often moved about by fork lifts which can impart enough force topull through the stretch over-wrap and destroy the integrity of theunitized pallet of goods.

Further, the tackifiers tend to be expensive and add to the cost of theoverall film structure. The migratory tackifiers tend to be difficult touse for single-sided stretch cling film structures. Of particularconcern, the migration of the tackifiers is subject to the duration oftime since the film was made, the temperature under which the film wasmade and stored, the molecular characteristics (such as the molecularweight) of the base resin to which they are added, and the processingconditions utilized for over-wrapping the goods, such as windingtension. These result in films exhibiting widely divergent clingproperties based on the properties present during their manufacture,storage and use. It also makes it difficult to use a single tackifier tomanufacture a variety of different single-sided stretch cling films, ofwhich each are designed to utilize different base polyethylene resin forthe cling layer. Since the tackifiers are typically low molecular weightand amorphous, they can be difficult to handle in the context of typicalthermoplastic film forming operations and can require specializedhandling equipment, which adds to the complexity needs for manufacturingthe single-sided stretch cling film. An additional layer can be providedbetween the cling and the release layer that comprises a thermoplasticresin that acts as a barrier to the migration of the tackifier. However,this additional layer further adds to the cost and complexity ofmanufacturing the film.

Single-sided stretch cling films have been disclosed wherein the clinglayer comprises functionalized polymers, such as ethylene acrylateand/or ethylene vinyl acetate copolymers. While the functionalizedpolymers tend to improve the cling properties of the film, they alsotend to be incompatible with the base resin making up the majority ofthe cling layer. This incompatibility can result in rheology matchingproblems in co-extrusions with polyethylene as well as thermalinstability. Additionally, these functionalized polymers can lead toincompatibility problems during recycling of edge trim and film scrapgenerated during the film fabrication process. Further, thefunctionalized polymers are expensive and can greatly increase the costfor manufacturing the films.

What is desired is a composition that does not need to contain amigratory tackifier or functionalized polymers but, when incorporatedinto the cling layer of a single-sided stretch cling film, results infilm that provides adequate cling properties, but also exhibitsacceptably low noise when the film is unwound from film supply rollduring over-wrapping operations. Additionally, it is desirable that thecomposition comprise at least 80 percent by weight of a polyethylenehaving a density of at least 0.905 g/cc. Further, it is desirable thatthe composition contains a non-migratory cling additive that will beuseful for providing acceptable cling properties across a wide varietyof different polyethylene base resins.

OBJECTS OF THE INVENTION

One object of the invention is to provide a composition useful forincorporation include the cling layer of a single-sided stretch clingfilm structure that can be manufactured with substantially reduced, oreliminated, die-lip build-up, and little or no accumulation of lowmolecular weight materials.

Another object of the invention is to provide a single-sided stretchcling film structure that can be manufactured with substantially reducedor eliminated die-lip build-up and accumulation of low molecular weightmaterials.

Still another object of the invention is to provide a single-sidedstretch cling film comprising polymers with similar rheologies andmonomer chemistries, thereby facilitating improved melt viscositymatching during co-extrusion of the film, and good polymer compatibilityfor recycling purposes.

A further object of the invention is to provide a single-sided stretchcling film which exhibits acceptable cling characteristics understretched conditions and also generates acceptably low noise levelsduring over-wrapping operations.

Another further object of the invention is to provide a single-sidedstretch cling film that incorporate polymers that can impart clingproperties but don't exhibit migratory properties, hence showing moreconsistent cling performance over time.

DEFINITIONS

Single-sided stretch cling film: is a stretchable film having an outerlayer exhibiting substantial cling properties. This layer is oftenreferred to as the “cling” layer. The other outer layer of the film isthe release layer. The release layer may exhibit some cling properties,but they are less than those exhibited by the cling layer. In general,the cling force measured between two cling (A) layers of adjacent filmstructures and between the cling (A) layer of one film and the release(B) layer of another film, is much greater than the cling forceexhibited between the release (B) layer of one film and the release (B)layer of an adjacent film. The single-sided stretch cling film istypically wrapped around an article or group of articles to form aunitized package or “pallet.” The unitized package is at least partiallyheld together by the retaining force applied by over-wrap, which isstretched during the wrapping procedure. The package article or group ofarticles is typically wrapped so that the release layer of the film islocated on the side of the film away from the article and the clinglayer is located on the side of the film closest to the article.

SUMMARY

In a first embodiment, the invention is a composition suitable for usein a cling layer of a single-sided stretch cling film, the compositioncomprising:

-   -   A. from 0.1 to 20% by weight of a propylene-based copolymer        having substantially isotactic propylene sequences, the        propylene-based copolymer comprising propylene and from about 10        to about 33 mole % of units derived from an alpha olefin, the        propylene-based copolymer having a melt flow rate less than 50        g/10 min; and    -   B. from about 80 to about 99 % by weight of a ethylene-based        copolymer having a density of at least 0.905 g/cc, wherein a        film made from the composition exhibits cling layer to release        layer cling of at least 70 grams force per inch as measured by        ASTM D-5458-95, noise levels of less than 87 dB during unwinding        operations, and has a modulus of at least 3 MPA as determined by        ASTM D 882.

In a second embodiment, the invention is a composition suitable for usein a cling layer of a single-sided stretch cling film, the compositioncomprising:

-   -   A. from 4 to 12% by weight of a propylene-based copolymer having        substantially isotactic propylene sequences, the propylene-based        copolymer comprising propylene and from about 10 to about 17 wt        % of units derived from ethylene, the propylene-based copolymer        having a melt flow rate from about 3 to about 18 g/10 min and        exhibiting a heat of fusion of less than about 25 Joules/gram;        and    -   B. from about 88 to about 96 % by weight of a ethylene/1-octene        copolymer having a density of at least 0.917 g/cc and a melt        index of from about 2 to about 12 g/10 min.

In a third embodiment, the invention is a single-sided stretch film, thefilm comprising:

-   -   A. a cling layer comprising:        -   (1) from 0.1 to 20% by weight of a propylene-based copolymer            having substantially isotactic propylene sequences, the            propylene-based copolymer comprising propylene and from            about 10 to about 33 mole % of units derived from an alpha            olefin, the propylene-based copolymer having a melt flow            rate less than 50 g/10 min; and        -   (2) from about 80 to about 99 % by weight of a            ethylene-based copolymer having a density of at least 0.905            g/cc; and    -   B. a release layer comprising a polyethylene having a density of        at least 0.905 g/cc,

wherein the film exhibits a cling layer to release layer cling of atleast 70 grams force per inch as measured by ASTM D-5458-95, noiselevels of less than 87 dB during unwinding operations, and has a modulusof at least 3 MPA as determined by ASTM D-882.

FIGURES

FIG. 1 shows the 13C NMR Spectrum of a propylene-ethylene copolymer(made with an activated non-metallocene, metal centered, heteroarylligand catalyst similar to Catalyst A), which is similar to thepropylene-ethylene copolymers used in the Examples.

FIG. 2 shows the 13C NMR Spectrum of same propylene-ethylene copolymeras FIG. 1. However, the spectrum is shown with an expanded Y-axis scalerelative to FIG. 1, in order to more clearly show the regio-error peaksat about 14.6 and 15.7 ppm.

FIG. 3 shows the ¹³C NMR Spectrum of a propylene-ethylene copolymerprepared using a metallocene catalyst. The figure demonstrates theabsence of regio-error peaks in the region around 15 ppm for apropylene-ethylene copolymer made with a metallocene catalyst.

FIG. 4 is a graphical depiction showing the noise versus cling levelsexhibited by the single-sided stretch cling films of Examples 3 through7.

FIG. 5 is a graphical depiction showing the noise and cling levelsexhibited by the single-sided stretch cling films of Examples 3 through13.

FIG. 6 is a graphical depiction showing the noise and cling levelsexhibited by the single-sided stretch cling films of Examples 8, 14through 22.

FIG. 7 is a simplified depiction of an apparatus useful for measuringthe unwinding noise levels generated by a cling film.

DETAILED DESCRIPTION

Polyethylene for the Cling Layer:

The polyethylene used in the cling layer preferably is a copolymer ofunits derived from ethylene and an alpha-olefin comonomer and preferablyhas a density of at least 0.905 g/cc, more preferably at least 0.910g/cc, further more preferably at least 0.915 g/cc, most preferably atleast 0.917 g/cc, and in some instances, such as where very high modulusfilms are desired, preferably at least 0.920 g/cc. The density of thepolymers used in the current invention is measured in accordance withASTM D-792.

The preferred alpha-olefin comonomers are C3 to C10 alpha-olefins, morepreferably C4-C8 alpha-olefins, further more preferably C4, C5, C6 andC8 alpha-olefins, most preferably 1-butene, 1-hexene and 1-octene. Dueto their superior film strength properties (such as tear resistance,puncture resistance, holding force and dart impact strength), thepolyethylene copolymers preferably are linear polyethylenes made usinggas phase, solution, or slurry polymer manufacturing processes, as knownto one of ordinary skill in the art. Examples of polyethylenes usefulfor the cling layer are ethylene/1-octene substantially linearcopolymers available from The Dow Chemical Company under the tradename“AFFINITY”, ethylene/1-octene and ethylene/1-hexene linear copolymersavailable from The Dow Chemical Company under the tradename “DOWLEX”,ethylene/1-octene linear copolymers available from The Dow ChemicalCompany under the tradename “ATTANE”, ethylene/1-octene enhancedpolyethylene available from The Dow Chemical Company under the tradename“ELITE”, ethylene-based copolymers available from Polimeri Europa underthe tradenames “CLEARFLEX” and “FLEXIRENE”, ethylene/alpha-olefincopolymers available from ExxonMobil Chemical under the tradenames“Escorene”, “Exact” and “Exceed”, ethylene/alpha-olefin copolymersavailable from BP Petrochemicals under the tradename “INNOVEX”,ethylene/alpha-olefin copolymers available from Basell under thetradenames “TUFLEXEN” and “LUPOLEX”, ethylene/alpha-olefin copolymersavailable from DSM under the tradename “STAMYLEX”, andethylene/alpha-olefin copolymers available from Sabic under thetradename “LADENE.

The melt index (“MI”) of the polyethylene useful in the cling layerdepends upon the method contemplated to be used for manufacturing thesingle-sided stretch cling film. In general, the typical melt index isfrom 0.1 to 20 g/10 min. For films made using blown film manufacturingmethods as known to one of ordinary skill in the art, the melt indexpreferably is from 0.3 to 9 g/10 min, more preferably from 0.5 to 6 g/10min, most preferably from 1 to 3 g/10 min. For films made using castfilm manufacturing methods as known to one of ordinary skill in the art,the melt index preferably is from 1 to 15 g/10 min, more preferably from2 to 12 g/10 min, most preferably from 3 to 8 g/1 0 min. Melt index (MI)measurement is performed according to ASTM D-1238, Condition 190°C./2.16 kilogram (kg) weight, formerly known as “Condition E” and alsoknown as I2. Melt index is inversely proportional to the molecularweight of the polymer. Thus, the higher the molecular weight, the lowerthe melt index, although the relationship is not linear.

Base Polymer for the Release Layer:

The polymer for the release (B) layer imparts to the film structure arelease (sometimes referred to as “slip”) surface. While anythermoplastic or blends thereof can be employed which will providesufficient release properties, polyolefins preferably are utilized inthis layer. More preferably, polyethylenes are utilized in this layer:For ease of handling, manufacture and recyclability, the polyethylenethat is used in the release layer is the same or similar to thepolyethylene used in the cling layer and, if used, the core (C) layer.This will be particularly useful for recycling of scrap. Forsingle-sided stretch cling films having higher stretch force andmodulus, polyethylene having a density of at least 0.917 g/cc preferablyare utilized, more preferably at least 0.920 g/cc and in some instancespreferably at least 0.925 g/cc.

Propylene-Based Copolymer:

The propylene-based copolymer comprises from 0.1 to 20 percent by weightof the total polymer composition capable of being utilized for the clinglayer. Preferably, the propylene-based copolymer comprises from 1 to 15percent by weight of the total composition, capable of being utilizedfor the cling layer, more preferably from 3 to 12 percent by weight ofthe total polymer composition, further more preferably from 4 to 12percent by weight.

The propylene-based copolymer of the current invention is characterizedas having substantially isotactic propylene sequences. “Substantiallyisotactic propylene sequences” and similar terms mean that the sequenceshave an isotactic triad (mm) measured by ¹³C NMR of greater than about0.85, preferably greater than about 0.90, more preferably greater thanabout 0.92 and most preferably greater than about 0.93. Isotactic triadsare well-known in the art and are described in, for example, U.S. Pat.No. 5,504,172 and WO 00/01745, which refer to the isotactic sequence interms of a triad unit in the copolymer molecular chain determined by ¹³CNMR spectra. NMR spectra are determined as described below.

The propylene-based copolymer of the invention have a melt flow rate(MFR) of less than 50 g/10 min which correlates to a weight averagemolecular weight (Mw) of greater than 100,000. It is believed that thecombination of the relatively high isotacticity index, the relativelylow melt flow rate (which corresponds to a relatively high weightaverage molecular weight), and preferably a crystallinity of at least 1percent by weight (a heat of fusion of at least 1.65 Joules/grain), morepreferably at least 2 percent by weight (a heat of fusion of at least3.3 Joules/gram) result in the propylene-based polymer beingnon-migratory under most film processing conditions. This non-migratorynature will result in single-sided stretch cling film structures inwhich the cling properties of the cling layer are relatively constantover time and are not highly dependent on the processing conditionsutilized to manufacture the film, or the conditions utilized forover-wrapping a group of goods to be unitized. Additionally, thenon-migratory nature of the propylene-based copolymer will enable thepolymer to be readily blended with a variety of polyethylenes and beincorporated into a variety of different film designs and still enablethe single-sided stretch cling films to exhibit excellent clingproperties and generate low noise when used in pallet over-wrappingoperations.

In order to provide enhanced cling properties, the crystallinitypreferably is less than 40 percent by weight (a heat of fusion of lessthan 69 Joules/gram), more preferably less than 30 percent by weight (aheat of fusion of less than 51 Joules/gram), further more preferablyless than 15 percent by weight (a heat of fusion of less than 25Joules/gram), and where handling is not a problem (i.e. sticky polymerscan be utilized) preferably less than 7 percent by weight (a heat offusion of less than 11 Joules/gram), even more preferably less than 5percent by weight (a heat of fusion of less than 8.3 Joules/gram)determined in accordance with DSC method described below.

The propylene-based copolymer of the invention is comprised of unitsderived from propylene and from polymeric units derived fromalpha-olefins. The preferred comonomers utilized to manufacture thepropylene-based copolymer are C2, and C4 to C10 alpha-olefins,preferably C2, C4, C6 and C8 alpha-olefins, most preferably ethylene.

The propylene-based copolymer of the invention preferably comprises from10 to 33 mole percent units derived from the alpha-olefin comonomer,more preferably from 13 to 27 mole percent units derived from thealpha-olefin comonomer. When ethylene is the comonomer, thepropylene-based copolymer preferably comprises from 7 to 25 weightpercent units derived from ethylene, more preferably from 9 to 20 weightpercent units derived from ethylene, further more preferably from 10 to17 weight percent units derived from ethylene, most preferably from 11to 16 weight percent units derived from ethylene.

¹³C NMR spectroscopy is one of a number of techniques known in the artof measuring comonomer incorporation into a polymer and measuringisotactic triad levels in propylene-based copolymers. An example of thistechnique is described for the determination of comonomer content forethylene/α-olefin copolymers in Randall (Journal of MacromolecularScience, Reviews in Macromolecular Chemistry and Physics, C29 (2 & 3),201-317 (1989)). The basic procedure for determining the comonomercontent of an olefin interpolymer involves obtaining the ¹³C NMRspectrum under conditions where the intensity of the peaks correspondingto the different carbons in the sample is directly proportional to thetotal number of contributing nuclei in the sample. Methods for ensuringthis proportionality are known in the art and involve allowance forsufficient time for relaxation after a pulse, the use ofgated-decoupling techniques, relaxation agents, and the like. Therelative intensity of a peak or group of peaks is obtained in practicefrom its computer-generated integral. After obtaining the spectrum andintegrating the peaks, those peaks associated with the comonomer areassigned. This assignment can be made by reference to known spectra orliterature, or by synthesis and analysis of model compounds, or by theuse of isotopically labeled comonomer. The mole % comonomer can bedetermined by the ratio of the integrals corresponding to the number ofmoles of comonomer to the integrals corresponding to the number of molesof all of the monomers in the interpolymer, as described in Randall, forexample.

The data is collected using a Varian UNITY Plus 400 MHz NMRspectrometer, corresponding to a ¹³C resonance frequency of 100.4 MHz.Acquisition parameters are selected to ensure quantitative ¹³C dataacquisition in the presence of the relaxation agent. The data isacquired using gated ¹H decoupling, 4000 transients per data file, a 7sec pulse repetition delay, spectral width of 24,200 Hz and a file sizeof 32K data points, with the probe head heated to 130° C. The sample isprepared by adding approximately 3 mL of a 50/50 mixture oftetrachloroethane-d2/orthodichlorobenzene that is 0.025M in chromiumacetylacetonate (relaxation agent) to 0.4 g sample in a 10 mm NMR tube.The headspace of the tube is purged of oxygen by displacement with purenitrogen. The sample is dissolved and homogenized by heating the tubeand its contents to 150° C. with periodic refluxing initiated by heatgun.

Following data collection, the chemical shifts are internally referencedto the mmmm pentad at 21.90 ppm.

For propylene-ethylene copolymers, the following procedure is used tocalculate the mole percent ethylene in the polymer. Integral regions aredetermined as follows: TABLE A Integral Regions for Determining %Ethylene Region designation PPM A 44-49 B 36-39 C 32.8-34   P 31.0-30.8Q Peak at 30.4 R Peak at 30   F 28.0-29.7 G   26-28.3 H 24-26 I 19-23

Region D is calculated as D=P×(G×Q)/2. Region E=R+Q+(G×Q)/2. TABLE ECalculation of Region D PPP = (F + A − 0.5 D)/2 PPE = D EPE = C EEE = (E− 0.5 G)/2 PEE = G PEP = H Moles P = sum P centered triads Moles E = sumE centered triads Moles P = (B + 2A)/2 Moles E = (E + G + 0.5 B + H)/2

C2 values are calculated as the average of the two methods above (triadsummation and algebraic) although the two do not usually vary. Theweight percent of units derived from ethylene in the propylene-ethylenecopolymers can be calculated from the values for mole percent ethyleneby one of ordinary skill in the art.

In a particularly preferred aspect of the invention, the propylene-basedcopolymer utilized in the invention comprises a propylene-ethylenecopolymer made using a nonmetallocene, metal-centered, heteroaryl ligandcatalyst as described in U.S. patent application Ser. No. 10/139,786filed May 5, 2002 (WO 03/040201), which is incorporated by referenceherein in its entirety for its teachings regarding such catalysts. Forsuch catalysts, the term “heteroaryl” includes substituted heteroaryl.An example of such a nonmetallocene, metal-centered, heteroaryl ligandcatalyst is Catalyst A described in the Examples. The propylene-ethylenecopolymers made with such nonmetallocene, metal-centered, heteroarylligand catalyst exhibit a unique regio-error. The regio-error isidentified by ¹³C NMR peaks corresponding at about 14.6 and about 15.7ppm, which are believed to be the result of stereo-selective2,1-insertion errors of propylene units into the growing polymer chain.In this particularly preferred aspect, these peaks are of about equalintensity, and they typically represent about 0.02 to about 7 molepercent of the propylene insertions into the homopolymer or copolymerchain.

A comparison of several ¹³C NMR spectra further illustrates the uniqueregio-errors of propylene-ethylene copolymers preferably utilized in theparticularly preferred aspect of the invention. FIGS. 1 and 2 are thespectra of the propylene-ethylene copolymers similar to thepropylene-ethylene copolymers utilized in the Examples. The spectrum ofeach polymer reports a high degree of isotacticity (isotactic triad (mm)measured by ¹³C NMR of greater than 0.94) and the unique regio-errors ofthese propylene-ethylene based copolymers. The ¹³C NMR spectrum of FIG.3 is that of a propylene-ethylene copolymer prepared using a metallocenecatalyst. This spectrum does not report the regio-error (at about 14.6and about 15.7 ppm) characteristic of the most preferredpropylene-ethylene copolymers used in this invention.

Isotacticity at the triad level (mm) is determined from the integrals ofthe mm triad (22.70-21.28 ppm), the mr triad (21.28-20.67 ppm) and therr triad (20.67-19.74). The mm isotacticity is determined by dividingthe intensity of the mm triad by the sum of the mm, mr, and rr triads.For ethylene copolymers the mr region is corrected by subtracting37.5-39 ppm integral. For copolymers with other monomers that producepeaks in the regions of the mm, mr, and rr triads, the integrals forthese regions are similarly corrected by subtracting the intensity ofthe interfering peak using standard NMR techniques, once the peaks havebeen identified. This can be accomplished, for example, by analysis of aseries of copolymers of various levels of monomer incorporation, byliterature assignments, by isotopic labeling, or other means which areknown in the art.

In some aspects of the invention, the propylene based copolymer has amolecular weight distribution (MWD), defined as weight average molecularweight divided by number average molecular weight (Mw/Mn) of 3.5 orless.

Molecular weight distribution of the polymers is determined using gelpermeation chromatography (GPC) on a Polymer Laboratories PL-GPC-220high temperature chromatographic unit equipped with four linear mixedbed columns (Polymer Laboratories (20-micron particle size)). The oventemperature is at 160° C. with the autosampler hot zone at 160° C. andthe warm zone at 145° C. The solvent is 1,2,4-trichlorobenzenecontaining 200 ppm 2,6-di-t-butyl-4-methylphenol. The flow rate is 1.0milliliter/minute and the injection size is 100 microliters. About 0.2%by weight solutions of the samples are prepared for injection bydissolving the sample in nitrogen purged 1,2,4-trichlorobenzenecontaining 200 ppm 2,6-di-t-butyl-4-methylphenol for 2.5 hrs at 160° C.with gentle mixing.

The molecular weight determination is deduced by using ten narrowmolecular weight distribution polystyrene standards (from PolymerLaboratories, EasiCal PSI ranging from 580-7,500,000 g/mole) inconjunction with their elution volumes. The equivalentpropylene-ethylene copolymer molecular weights are determined by usingappropriate Mark-Houwink coefficients for polypropylene (as described byTh.G. Scholte, N. L. J. Meijerink, H. M. Schoffeleers, and A. M. G.Brands, J. Appl. Polym. Sci., 29, 3763-3782 (1984)) and polystyrene (asdescribed by E. P. Otocka, R. J. Roe, N. Y. Hellman, P. M. Muglia,Macromolecules, 4, 507 (1971)) in the Mark-Houwink equation:{N}=KM^(a)where K_(pp)=1.90E-04, a_(pp)=0.725 and K_(ps)=1.26E-04, a_(ps)=0.702.Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) is a common technique that canbe used to examine the melting and crystallization of semi-crystallinepolymers. General principles of DSC measurements and applications of DSCto studying semi-crystalline polymers are described in standard texts(e.g., E. A. Turi, ed., Thermal Characterization of Polymeric Materials,Academic Press, 1981). In the particularly preferred aspect of theinvention, propylene-ethylene copolymers are utilized in the inventionand are characterized by a DSC curve with a T_(me) that remainsessentially the same and a T_(max) that decreases as the amount ofunsaturated comonomer in the copolymer is increased. T_(me) means thetemperature at which the melting ends and T_(max) means the peak meltingtemperature, both as determined by one of ordinary skill in the art fromDSC analysis using data from the final heating step.

Differential Scanning Calorimetry (DSC) analysis is determined using amodel Q1000 DSC from TA Instruments, Inc. Calibration of the DSC is doneas follows. First, a baseline is obtained by running the DSC from −90°C. to 290° C. without any sample in the aluminum DSC pan. Then 7milligrams of a fresh indium sample is analyzed by heating the sample to180° C., cooling the sample to 140° C. at a cooling rate of 10° C./minfollowed by keeping the sample isothermally at 140° C. for 1 minute,followed by heating the sample from 140° C. to 180° C. at a heating rateof 10° C./min. The heat of fusion and the onset of melting of the indiumsample are determined and checked to be within 0.5° C. from 156.6° C.for the onset of melting and within 0.5 J/g from 28.71 J/g for the heatof fusion. Then deionized water is analyzed by cooling a small drop offresh sample in the DSC pan from 25° C. to −30° C. at a cooling rate of10° C./min. The sample is kept isothermally at −30° C. for 2 minutes andheated to 30° C. at a heating rate of 10° C./min. The onset of meltingis determined and checked to be within 0.5° C. from 0° C.

The propylene-based copolymers samples are pressed into a thin film at atemperature of 190° C. About 5 to 8 mg of sample is weighed out andplaced in the DSC pan. The lid is crimped on the pan to ensure a closedatmosphere. The sample pan is placed in the DSC cell and the heated at ahigh rate of about 100° C./min to a temperature of about 30° C. abovethe melt temperature. The sample is kept at this temperature for about 3minutes. Then the sample is cooled at a rate of 10° C./min to −40° C.,and kept isothermally at that temperature for 3 minutes. Consequentlythe sample is heated at a rate of 10° C./min until complete melting. Theresulting enthalpy curves are analyzed for peak melt temperature, onsetand peak crystallization temperatures, heat of fusion and heat ofcrystallization, T_(me), and any other DSC analyses of interest. Thefactor that is used to convert heat of fusion into nominal weight %crystallinity is 165 J/g=100 weight % crystallinity. With thisconversion factor, the total crystallinity of a propylene-basedcopolymer (units: weight % crystallinity) is calculated as 100% timesheat of fusion divided by 165 J/g.

The melt flow rate (“MFR”) of the propylene-based copolymer useful forthe cling layer depends upon the method contemplated to be used formanufacturing the single-sided stretch cling film. In general, thetypical melt flow rate is from 0.1 to 50 g/10 min. For films made usingblown film manufacturing methods as known to one of ordinary skill inthe art, the melt flow rate preferably is from 0.5 to 12 g/10 min, morepreferably from 1 to 10 g/10 min, most preferably from 2 to 9 g/10 min.For films made using cast film manufacturing methods as known to one ofordinary skill in the art, the melt flow rate preferably is from 2 to 25g/10 min, more preferably from 3 to 18 g/10 min, most preferably from 5to 12 g/10 min. Melt flow rate (MFR) measurement is performed accordingto ASTM D-1238, Condition 230° C./2.16 kilogram (kg) weight. As with themelt index, the melt flow rate is inversely proportional to themolecular weight of the polymer. Thus, the higher the molecular weight,the lower the melt flow rate, although the relationship is not linear.

Single-Sided Stretch Cling Film:

The single-sided stretch cling film of the present invention can bestretched by more than 100%, preferably by more than 200%, of itsoriginal, unstretched length, more preferably between 250 and 450%, asmeasured by ASTM D4649-03. The single-sided stretch cling film of thepresent invention exhibits cling layer-to-release layer cling of atleast 70 grams-force per inch, preferably at least 80 grams-force perinch, more preferably at least 100 grams-force per inch, further morepreferably at least 120 grams-force per inch, most preferably at least150 grams-force per inch, and in some instances at least 200 grams-forceper inch as measured in accordance with ASTM D-5458-95, which is a peelcling procedure where a one inch (25mm) wide strip of film is adhered toa flat film attached to an inclined surface. The force required toremove the film strip from the flat film is measured. Cling values fromthe test are reported in grams-force per inch. The cling force of acling layer of the single-sided stretch cling film of this invention toanother cling layer of a similar film (of identical composition)preferably is between 150 grams-force per inch and 400 grams-force perinch. The single-sided stretch cling film of the present invention alsogenerates peak noise levels of less than 87 dB, measured as described inthe examples with a microphone located 10 cm from the unwinding 500 mmwide film rolls containing 23 micron thick film (with a backgroundenvironmental noise level of 45 dB), and with a film unwinding speed of110 meters/minute. Preferably, under-these conditions the noise levelsgenerated during unwinding operations is less than 85 dB, morepreferably less than 83 dB, further more preferably less than 82 dB,most preferably less than 80 dB, and in some instances less than 79 dB.

The release layer exhibits less cling to itself than to the cling layer.In general, the cling of one release layer to another release layer isat most 60 grams-force per inch, preferably at most 20 grams-force perinch, as measured following ASTM D-5458-95 on an unstretched film.Preferably, the coefficient of friction of the release layer to itselfis below 1, and is typically in the range of 0.15 to 0.7, preferably0.25 to 0.5. A low coefficient of friction and non-cling behavior forthe release layer is particularly desirable where products wrapped withthe film may touch or slide against each other. Surprisingly, it hasbeen discovered that a small amount of propylene-based copolymer may beincorporated into the release layer without unduly affecting theproperties of the release layer and/or the interactions between therelease layer and cling layer. In particular, up to 2% by weight of apropylene-based copolymer, preferably a propylene-ethylene copolymermade with a nonmetallocene metal-centered heteroaryl ligand catalyst asdescribed above, may be incorporated into the release layer when it isdesirable to enhance the cling properties between the cling layer andthe release layer, while at the same time not unduly affecting therelease properties.

The single-sided stretch cling film of the invention typically exhibitsa machine direction (“MD”) tensile strength from about 3 to 15 MPa., asmeasured by ASTM D-882. Preferably, the machine direction tensilestrength is at least 6 MPa. more preferably at least 7 MPa further morepreferably at least 8MPa., most preferably at least 9 Mpa, and in someinstances where tensile strength is particularly important (such aswhere extreme down gauging is desirable and/or where it is desirable toutilize a film which is capable of developing extreme holding forces) atleast 15 MPa.

The multilayer single-sided stretch cling film of the present inventionmay be constructed from two or more film layers, including A/B and A/C/Btype film structures by any film lamination and/or coextrusion techniqueand using any blown or cast film extrusion and lamination equipmentknown in the art. The preferred multilayer film structures are preparedusing coextrusion techniques, and more preferably, by cast coextrusiontechniques. For simplicity and ease of manufacture A/B type filmstructures are preferred. By convention for the invention, A will referto the cling layer in A/B and A/C/B structures exemplified herein. Therelease layer will be designated by B.

If utilized, the C layer can comprise one or more additional layers thatare utilized to modify some property or properties of the filmstructure, compared to the A/B film structure. In many commercial filmstructures the C layer/s is a main part of the entire film, typically itadds up to more than 30 percent by weight of the entire structure, morepreferably 50 to 70 percent by weight and most preferably 60 to 90percent by weight. In general, the materials chosen for core (C)layer(s) can have a great effect on the overall mechanical properties ofthe resulting single-sided stretch cling film. The polymers chosen forthe core layer(s) are typically polyethylene polymers. If a higherstiffness film is desirable in order to develop greater holding forcewhen stretched, then higher crystallinity ethylene copolymer (having adensity of at least 0.917 g/cc, preferably at least 0.920 g/cc, morepreferably at least 0.925 g/cc.) is utilized in the core layer. If asofter film is desirable, then lower crystallinity ethylene copolymers(having a density of from 0.88 to 0.915 is utilized in the core layer.The use of lower crystallinity copolymers for the core will also resultin films with improved toughness and elasticity performance, but withlower holding force.

Since the C layer is encapsulated by the cling layer (A) and the releaselayer (B), a wide variety of polymers can be utilized in the core layer,which can be selected to improve selected properties of the film,without interfering with the cling and release properties of layers Aand B. Also, the use of a core layer, will allow film trimming and scrapfrom the film fabrication process to be recycled back into the corelayer, without adversely affecting the properties of the cling andrelease layers. For recycling purposes it is preferable to use the sameor similar polyethylene resins in the A, B, and C layers.

Due to the inherent cling and non-cling properties of the individuallayers of the single-sided stretch cling film of the invention, it isnot necessary to include in the cling layer and non-cling layeradditives such as low molecular weight tackifiers or slip and anti-blockagents, to impart cling or non-cling characteristics. Preferably, thefilm is essentially free of such additives, thereby avoiding theproblems commonly associated therewith. By “essentially free” of suchadditives we mean that the amounts of such additives, if present at all,is such that the cling or non-cling properties of the film are notappreciably changed. For instance, depending on the nature of the film,cling and/or anti-cling additives may be present in an amount of lessthan 500 ppm each based on the total weight of polymer in the film, andtypically considerably less than this, for instance less than 100 ppm orless than 50 ppm based on the total weight of the polymers whichcomprise the film. An example of where a slip and/or anti-block additivemay be present is when such additives are added to the propylene-basedcopolymer and/or polyethylene to reduce blocking of the polymer duringshipment. In this type of scenario, the slip and/or anti-block additiveswill be present in the final film, but at the low levels describedabove.

In another less preferred aspect, anti-block and/or slip additives maybe added to the release layer, in order to improve the releaseproperties of the B layer. Non-limiting examples of anti-block additivesinclude formulations based on CaCO3 and/or SiO2. Non-limiting examplesof slip additives include formulations based on ercucamide and/oroleamide. If added, these anti-block and/or slip additives should be atsuch a level that they do not adversely affect the cling properties ofthe cling layer to the release layer, as described herein.

In addition to anti-block and/or slip additives, other additives such asfillers (mineral particles, lithopone formulations), pigments (TiO2particles) and functional additives (for examples antistaticformulations) may be added to the release layer and/or to the corelayer(s) to improve desirable properties of the film. These additionaladditives may also provide release properties to the release layer.

It may, however, be desirable to include in the single-sided stretchcling film of the invention additives which change other properties ofthe film, for example, antioxidants, free-radical scavengers, colorants,and other processing aids.

Suitable blown film processes are described, for example, in TheEncyclopedia of Chemical Technology Kirk-Othmer, Third Edition, JohnWiley & Sons, New York, 1981, Vol. 16, pp. 416-417 and Vol. 18, pp.191-192. A suitable cast extrusion method is described, for example, inModem Plastics Mid-October 1989 Encyclopedia Issue, Volume 66, Number11, pages 256 to 257. Suitable coextrusion techniques and requirementsare described by Tom I. Butler in Film Extrusion Manual: Process,Materials, Properties, “Coextrusion”, Ch. 4, pp. 31-80, TAPPI Press,(Atlanta, Ga. 1992).

The total film thickness of the multilayer film typically is from 0.4 to2 mils (10 microns to 51 microns), preferably in the range of 0.6 to 1.5mils (15 microns to 38 microns) and more preferably, in the range of0.66 to 1.0 mils (17 microns to 25 microns).

The layer ratio for the A/B and the A/C/B multilayer films of thisinvention typically is from 1:5 to 5:1 ratio of A layer to B layer(A:B), preferably from 1:3 to 3:1 A:B, more preferably from 1.2:1 to1:1.2 (A:B), and most preferably 1.1:1 to 1:1.1 (A:B).

The use of single-sided stretch cling films for the over-wrap packagingof goods, and in particular, the unitizing of pallet loads, is asignificant commercial end use application. There are a variety ofover-wrapping techniques which are employed utilizing such single-sidedstretch cling films, including locating the pallet load to be wrappedatop a rotating platform. As the stretch wrap film is laid on about thegirth of the pallet load, the pallet load is rotated on its platform.The single-sided stretch cling film is applied from a continuous filmroll. Braking tension is applied to the continuous roll of film so thatthe film is being continuously stretched by the rotating pallet load.Usually the single-sided stretch cling film, located adjacent to therotating pallet load, is vertically positioned and the rotating platformor turntable may be operated at speeds ranging from about 5 up to about50 revolutions per minute. At the completion of the over-wrappingoperation, the turntable is stopped while the film is cut and attachedto the previous layer of film by employing tack sealing, adhesive tape,spray adhesives, pressure sealing, etc. Depending upon the width of thesingle-sided stretch cling film roll, the load being over-wrapped may beshrouded in the film while the vertically positioned film roll remainsfixed in a vertical position, or the vertically positioned film roll(for example in the case of relatively narrow film widths and relativelywider pallet loads) may be arranged to move in a vertical direction asthe load is being over-wrapped whereby a spiral wrapping effect isachieved on the packaged goods. Additional examples of pallet unitizingtechniques are described in U.S. Pat. Nos. 3,986,611 and 4,050,221,which are incorporated by reference herein for their disclosuresregarding pallet unitizing methods and techniques.

In addition to unitizing of pallet loads, additional uses forsingle-sided stretch cling films include: wrapping of silage bales andmetal and paper reels, collation wrapping of cardboard and plastic traysand profiles made from wood, plastics and metals.

EXAMPLES

The polymers disclosed in the examples are the following:

P-E 1 is a propylene-ethylene copolymer made as described below,containing 12 percent by weight units derived from ethylene and having amelt flow rate of 8 g/10 min. This copolymer exhibits a heat of fusionof 21.5 Joules/gram, which corresponds to a crystallinity of 13 wt %,and a MWD of 3. This propylene-ethylene copolymer exhibited triadisotacticity (mm) of 0.96.

P-E 2 is a propylene-ethylene copolymer made as described below,containing 15 percent by weight units derived from ethylene and having amelt flow rate of 8 g/10 min. This copolymer exhibits a heat of fusionof 8.0 Joules/gram, which corresponds to a crystallinity of 5 wt %, anda MWD of 3. This propylene-ethylene copolymer exhibited triadisotacticity (mm) of 0.96.

DOWLEX SC2107 is an ethylene/1-octene copolymer having a melt index of2.3 g/10 min and a density of 0.917 g/cc, which is available from TheDow Chemical Company.

CLEARFLEX CLDO is an ethylene/alpha-olefin copolymer having a melt indexof 3 g/10 min and a density of 0.90 g/cc, which is available fromPolimeri Europa.

Catalyst A

Synthesis of Catalyst A

Hafnium,[N-[2,6-bis(1-methylethyl)phenyl]-α-[2-(1-methylethyl)phenyl]-6-(1-naphthanlenyl-κ-C²)-2-pyridinemethanaminato(2-)-κN¹, κN²]dimethyl-

a) 2-Formyl-6-bromopyridine. This compound is synthesized according toliterature procedures, Tetrahedron Lett., (2001) 42, 4841.

b) 6-Bromo-2-(2,6-diisopropylphenyl)iminopyridine). A dry, 500 mL 3-neckround bottom flask is charged with a solution of2-formyl-6-bromopyridine (72.1 g, 383 mmol) and 2,6-diisopropylaniline(72.5 g, 383 mmol) in 500 mL of anhydrous toluene containing 0.3 nm poresize molecular sieves (6 g) and 80 mg of p-TsOH. The reactor is equippedwith a condenser, an over head mechanical stirrer and a thermocouplewell. The mixture is heated to 70° C. under N₂ for 12 h. Afterfiltration and removal of the volatiles under reduced pressure, a brownoil is isolated. Yield was 109 g, 81.9 percent.

GC/MS 346 (M⁺), 331, 289, 189, 173, 159, 147, 131, 116, 103, 91, 78.

c). 6-(1-Naphthyl)-2-[(2,6-diisopropylphenyl)imino]pyridine.Naphthylboronic acid (54.5 g, 316 mmol) and Na₂CO₃ (83.9 g, 792 mmol)are dissolved into 200 mL of degassed 1:1 H₂O/EtOH. This solution isadded to a toluene solution (500 mL) of6-bromo-2-(2,6-diisopropylphenyl)-iminopyridine (109 g, 316 mmol).Inside of a dry box, 1 g (0.86 mmol) oftetrakis(triphenyl-phosphine)palladium(0) is dissolved in 50 mL ofdegassed toluene. The solution is removed from the dry box and chargedinto the N₂ purged reactor. The biphasic solution is vigorously stirredand heated to 70° C. for 4-12 hours. After cooling to room temperature,the organic phase is separated, the aqueous layer is washed with toluene(3×75 mL), the combined organic extracts are washed with H₂O (3×200 mL)and dried over MgSO₄. After removing the volatiles under reducedpressure, the resultant light yellow oil is purified viarecrystallization from methanol to give a yellow solid. Yield 109 g,87.2 percent; mp 142-144° C.

¹H NMR (CDCl₃) δ 1.3 (d, 12H), 3.14 (m, 2H), 7.26 (m, 3H), 7.5-7.6 (m,5H), 7.75-7.8 (m, 3H), 8.02 (m 1H), 8.48 (m, 2H).

¹³C NMR (CDCl₃) δ 23.96, 28.5, 119.93, 123.50, 124.93, 125.88, 125.94,126.49, 127.04, 127.24, 128.18, 128.94, 129.7, 131.58, 134.5, 137.56,137.63, 138.34, 148.93, 154.83, 159.66, 163.86.

GC/MS 396 (M⁺), 380, 351, 337, 220, 207, 189, 147.

d) 2-Isopropylphenyl lithium. Inside an inert atmosphere glovebox,n-butyl lithium (52.5 mmol, 21 mL of 2.5M in hexanes) is added byaddition funnel over a period of 35-45 min to an ether solution (50 mL)of 2-isopropyl bromobezene (9.8 g, 49.2 mmol). After the addition iscomplete, the mixture is stirred at ambient temperature for 4 h. Then,the ether solvent is removed under vacuum overnight. The next day hexaneis added to the remaining white solid and the mixture filtered, washedwith additional hexane, and then vacuum dried. 2-Isopropylphenyl lithium(4.98 g, 39.52 mmol) is collected as a bright white powder. A secondcrop of product (0.22 g) is later obtained from a second filtration ofthe original hexane filtrant.

¹H NMR (d₈-THF) δ 1.17 (d, J=6.8 Hz, 6H), 2.91 (sept, J=6.8, 1H),6.62-6.69 (multiplets, 2H), 6.77 (d, J=7.3 Hz, 1H), 7.69 (multiplet,1H).

¹³C NMR (d₈-THF) δ 25.99, 41.41, 120.19, 122.73, 122.94, 142.86, 160.73,189.97.

e) 2-pyridinemethanamine,N-[2,6-bis(1-methylethyl)phenyl]-α-[2-(1-methylethyl)phenyl]-6-(1-naphthanlenyl).The imine, 6-(1-naphthyl)-2-[(2,6-diisopropylphenyl)imino]pyridine ofstep c) (2.20 g, 5.6 mmol) is magnetically stirred as a slurry in 60-70mL of dry ether under a nitrogen atmosphere. An ether solution of2-isopropylphenyl lithium (1.21 g, 9.67 mmol in 25 mL dry ether) isadded slowly using a syringe over a period of 4-5 min. After theaddition is complete, a small sample is removed, quenched with 1N NH₄Cland the organic layer analyzed by high pressure liquid chromatography(HPLC) to check for complete consumption of starting material. Theremainder of the reaction is quenched by the careful, slow addition of1N NH₄Cl (10 mL). The mixture is diluted with more ether and the organiclayer washed twice with brine, dried (Na₂SO₄), filtered, and stripped ofsolvent under reduced pressure. The crude product obtained as a thickred oil (2.92 g; theoretical yield=2.87 g) is used without furtherpurification.

¹H NMR (CDCl₃) δ 0.96 (d, J=6.6 Hz, 3H), 1.006 (d, J=6.8 Hz, 3H), 1.012(d, J=6.8 Hz, 6H), 1.064 (d, J=6.8 Hz, 6H), 3.21-3.34 (multiplets, 3H),4.87 (br s, NH, 5.72 (s, 1H), 6.98 (d, J=7.6 Hz, 1H) 7.00-7.20(multiplets, 7H), 7.23-7.29 (multiplets, 4H), 7.51 (d, J=7.1 Hz, 1H),7.60-7.65 (multiplets, 2H), 7.75 (multiplet, 1H), 8.18 (multiplet, 1H).

¹³C NMR (CDCl₃) δ 23.80, 24.21, 24.24, 24.36, 28.10, 28.81, 67.08,120.20, 122.92, 123.96, 124.42, 125.35, 125.81, 126.01, 126.28, 126.52,126.58, 126.65, 127.80, 128.52, 128.62, 129.25,131.82, 134.52, 136.81,138.82, 140.94, 143.37, 143.41, 146.66, 159.05, 162.97.

f) Hafnium,[N-[2,6-bis(1-methylethyl)phenyl]-α-[2-(1-methylethyl)phenyl]-6-(1-naphthanlenyl-κ-C²)-2-pyridinemethanaminato(2-)-κN¹, κN²]dimethyl-

A glass jar is charged with 8.89 mmol of the ligand from step e)dissolved in 30 mL toluene. To this solution is added 8.98 mmol ofn-BuLi (2.5 M solution in hexanes) by syringe. This solution is stirredfor 1 hour, then 8.89 mmol of solid HfCl₄ are added. The jar is cappedwith an air-cooled reflux condenser and the mixture is heated at refluxfor 1 hour. After cooling, 31.1 mmol of MeMgBr (3.5 equivalents, 3.0 Msolution in diethyl ether) are added by syringe and the resultingmixture stirred overnight at ambient temperature. Solvent (toluene,hexanes and diethyl ether) is removed from the reaction mixture using avacuum system attached to the drybox. Toluene (30 mL) is added to theresidue and the mixture filtered, and the residue (magnesium salts) iswashed with additional toluene (30 mL). Solvent is removed by vacuumfrom the combined toluene solution, and hexane is added, then removed byvacuum. Hexane is again added and the resulting slurry is filtered andthe product washed with pentane to give the desired product as a yellowpowder.

¹H NMR (C₆D₆): δ 8.58 (d, J=7.8 Hz, 1H), 8.25 (d, J=8.4 Hz, 1H), 7.82(d, J=7.5 Hz, 1H), 7.72 (d, J=6.9 Hz, 1H), 7.50 (d, J=8.1 Hz, 1H),7.36-7.27 (multiplets, 3H), 7.19-6.99 (multiplets, 7H), 6.82 (t, J=8.1Hz, 1H), 6.57 (s, 1H), 6.55 (d, J=7.8 Hz, 1H), 3.83 (septet, J=6.9 Hz,1H), 3.37 (septet, J=6.9 Hz, 1H), 2.89 (septet, J=6.9 Hz, 1H), 1.38 (d,J=6.6 Hz, 3H), 1.37 (d, J=6.9 Hz, 3H), 1.17 (d, J=6.9 Hz, 3H), 1.15 (d,J=7.2 Hz, 3H), 0.96 (s, 3H), 0.70 (s, 3H), 0.69 (d, J=5.4 Hz, 3H), 0.39(d, J=6.9 Hz, 3H).

General Continuous Loop Solution Propylene-Ethylene CopolymerizationProcedure

The propylene-ethylene copolymers of Examples 1-24 (P-E 1, P-E 2, andP-E 3) are made according to the following procedure. Catalyst A is usedto manufacture all the propylene-ethylene copolymers of Examples 1-24.

The polymerization process is exothermic. There are 900 BTU released perpound of propylene polymerized and ˜1,500 BTU released per pound ofethylene polymerized. The primary process design consideration is how toremove the heat of reaction. The propylene-ethylene copolymers ofExamples 1-24 are produced in a low-pressure, solution polymerizationloop reactor, made up of a 3″ loop pipe plus two heat exchanges, thetotal volume of which is 31.4 gals. Solvent and monomer (propylene) areinjected into the reactor as a liquid. The comonomer (ethylene) gas isfully dissolved in the liquid solvent. The feed is cooled to 5° C.before injection into the reactor. The reactor operates at polymerconcentrations equal to 18 wt %. The adiabatic temperature rise of thesolution accounts for some of the heat removal from the polymerizationreaction. Heat exchangers within the reactor are utilized to remove theremaining heat of reaction, allowing for reactor temperature control at105° C.

The solvent used is a high purity iso-paraffinic fraction purchased fromExxon called Isopar E. Fresh propylene is passed through a bed ofSelexsorb COS for purification before mixing with the recycle stream(contains solvent, propylene, ethylene, and hydrogen). After mixing withthe recycle stream, the combined stream is passed through a bed of 75 wt% Molecular Sieve 13X and 25 wt % Selexsorb CD for further purificationbefore using a high pressure (700 psig) feed pump to pump the contentsto the reactor. Fresh ethylene is passed through a Selexsorb COS bed forpurification before compressing the stream to 750 psig. Hydrogen (atelogen used to reduce molecular weight) is mixed with the compressedethylene before the two are mixed/ dissolved into the liquid feed. Thetotal stream is cooled to the appropriate feed temperature (5° C.). Thereactor operates at 525 psig and a control temperature equal to 105° C.The propylene conversion in the reactor is maintained by controlling thecatalyst injection rate. The reaction temperature is maintained bycontrolling the water temperature across the shell side of the heatexchanger at 85° C. The residence time in the reactor is short, 10minutes. The propylene conversion per reactor pass is 60 wt %.

Upon exiting the reactor, water and additive are injected into thepolymer solution. The water hydrolyzes the catalyst, terminating thepolymerization reaction. The additives consist of antioxidants, 500 ppmof Irganox™ 1010 and 1000 ppm of Irgafos™ 168, that remain with thepolymer and act as stabilizers to prevent polymer degradation while instorage before subsequent fabrication at the end-user's facility. Thepost-reactor solution is super-heated from reactor temperature to 230°C. in preparation for a two-stage devolatilization. The solvent andunreacted monomers are removed during the devolatilization process. Thepolymer melt is pumped to a die for underwater pellet cutting.

Solvent and monomer vapors exiting the top of the devolatilizers aresent to a coalescer. The coalescer removes polymer entrained in thevapor during devolatilization. The clean vapor stream leaving thecoalescer is partially condensed through a series of heat exchangers.The two-phase mixture enters a separation drum. The condensed solventand monomers are purified (this is the recycle stream described above)and re-used in the reaction process. The vapors leaving the separatingdrum, mostly containing propylene and ethylene are sent to a block flareand burned.

Blending of the Cling Layer Components:

The compositions incorporated into the cling layer can be made by: (a)dry Blending of the component pellets; (b) direct feeding of thecomponent pellets via a blender system (volumetric or gravimetric)mounted on an extruder; (c) compounding the pellet components in acompounding extruder producing pellets of compounded product; and/or (d)any other blending techniques known to one of ordinary skill in the art.

Examples 1-2

The multilayer single-sided stretch cling films of Examples 1 and 2 areprepared using Dowlex SC2107 as the release layer (layer B), DowlexSC2107 as the core layer (layer C) and a blend of Dowlex SC2107 and apropylene-ethylene copolymer (P-E 1 or P-E 2) in the cling layer (layerA). The percent by weight of Dowlex SC2107 and propylene-ethylenecopolymer utilized for the cling layer is set forth in Table 1. The castco-extrusion film equipment utilized to prepare these single-sidedstretch cling films consists of a three extruder configuration: a 75 mmdiameter 30 L/D Primplast extruder (“C” core layer) with two 30:1 L/D55mm diameter Primplast satellite extruder (“A and B” cling layer andrelease layer). The molten polymer exits the extruders through an A/C/Bfeedblock into a 790 mm Er-We-Pa, flat film die. In manufacturing thefilms, the pumping rates of the extruders are adjusted to maintain a 15percent/70 percent/15 percent layer thickness ratio as molten polymer isfed through a 0.020 inch (0.05 cm) die gap. The co-extruded filmscontact two chill rolls cooled to 70° F. (21° C.) at an air/draw gap of5 inches (12.7 cm).

The cast co-extruded film samples are conveniently produced at a nominaltotal film thickness of 0.9 mil (23 microns), a melt temperature ofapproximately 482° F. (250° C.) for the A layer and 482° F. (250° C.)for B and C layers, and a line speed of 820 feet per minute (250 metersper minute). The resultant film has an unstretched releaselayer-to-cling layer cling value of ˜200 grams-force per inch accordingto ASTM D-5458-95. The resultant inventive films also exhibit acceptablecling values when the films are stretched to approximately 200 percentof their original length and tested in accordance with ASTM D-5458-95.

Comparative multilayer single-sided stretch cling films (CS-1 and CS-2)are made in the same manner as the inventive films using the materialsindicated in Table 1.

During the fabrication process, the films of Examples 1 and 2 exhibitexcellent extrusion processability, with no die-lip build-up observableduring a 2-hour fabrication trial. TABLE 1 Example Layer A Layer B LayerC 1 90 wt % Dowlex SC2107 + Dowlex Dowlex SC2107 10 wt % P-E 1 SC2107 295 wt % Dowlex SC2107 + Dowlex Dowlex SC2107 5 wt % P-E 2 SC2107 CS1Dowlex SC2107 70 wt % + Dowlex Dowlex SC2107 Polimeri CLDO 30 wt %SC2107 CS2 Dowlex SC2107 Dowlex Dowlex SC2107 SC2107

The cling films of Examples 1-2, and CS 1 and 2 are tested for clingproperties in accordance with ASTM D 5458-95, Test Methods for PeelCling of Stretch Wrap Film. The films are tested, release layer-to-clinglayer cling. The values for cling are reported in Table 2 as the forcein grams per inch width (g-force/inch) required to remove a film strip,one inch wide, from a flat film surface.

In order to determine the cling layer-to-release layer cling values(reported in Tables 2 and 4), a 1 inch (Transverse Direction) by 7 inch(Machine Direction) (25 mm by 178 mm) strip of film is cut and attachedto a 20 degree inclined plane with the release layer facing upward. Asecond, un-stretched 1 inch by 7 inch strip of film is placed on top ofthe first strip with the cling layer facing downward. Sufficientpressure is applied with a brush to cause the two strips to adheretogether. The end of the second strip at the base of the include planeis attached, by a clip and a string, to an apparatus which can exert astrain at a constant rate, such as an Instron Tensile Tester. The twostrips are separated at a crosshead speed of 5 inches per minute (13centimeters/minute) until the attached string is parallel with the baseof the inclined plane. The value for cling is determined at the momentwhen the 25.4 mm (1.0-in) film specimen is separating from the inclineat the horizontal cling line marked upon the incline face. The clinglevel, by convention, is reported in Tables 2 and 4 in units of gramsforce per inch. In order to determine stretched cling values, theprocedure is repeated with fresh film samples and is carried out asdescribed above, except the lower film is stretched to 200 percent itsoriginal length prior to being attached to the included plane. Ingeneral, stretched cling values are appreciably less than un-stretchedcling values.

Single-sided stretch cling films corresponding to the films of Examples1 and 2 are tested for noise generation during the unwinding of filmrolls that occurs during film over-wrapping operations carried-out inaccordance with the following method.

Procedure to Measure the Unwinding Noise Level with a Highlight Tester

Referring to FIG. 7, the test consists of stretching a 500 mm wide, 23micron thick single-sided cling film at a target elongation (pre-setstretch) of 200%. The stretching takes place between the Brake rollerand a Traction roller that are separated so that the stretching of thefilm takes place over a 16.0cm distance. Stretch film is obtained byrunning the traction roller at a higher rpm than the brake roller. Themachine measures sequentially, each second, stretching force and noiselevel. The film unwinding speed is 110 meters per minute and the noiselevels are measured with a microphone located tangentially to the filmroll at 10 cm from the film roll. The background environmental noise is45 dB.

The Noise meter utilized is a QUEST TECHNOLOGIES, Model 2700.

Unwinding force is measured with a load cell placed on the roller #1.Stretch force is measured with a load cell placed on roller #2. TABLE 2Example 1 2 CS1 CS2 Cling g-force/inch 198.4 201.6 106.5 55 Averagethickness μ 23 23 23 23 Maximum Stretch % 266 281 279 260 MaximumStretch Kg 36.7 36.7 35.7 35 Force Maximum Unwind Kg 3.1 2 1.6 1 forceAverage Stretch % 203 207 193 200 Average Stretch Kg 30.2 30.5 29.3 30Force Pre-set stretch % 200 200 200 200 Sound level Db 78.4 78.2 78.4 *MD Tensile Strength MPa 9 9 9 9 by ASTM D882

The data in Table 2 demonstrates that films prepared using theanti-cling composition of the present invention exhibit substantialcling while also exhibiting low noise generation during over-wrappingoperations. Surprisingly, single-sided stretch cling films made inaccordance with the current invention exhibited cling of greater than150 grams-force per inch, while also generating less than 80 dB ofnoise. Additionally, the films provide these benefits while at the sametime being able to develop excellent holding force (as exhibited by thehigh values of machine direction (MD) tensile force). The high tensileforces exhibited will enable the films of the invention to effectivelyunitize various products. Also, the excellent holding forces exhibitedby the inventive films will allow for the thickness of the film to bedown-gauged, while still providing adequate holding forces. The measuredcling properties develop relatively quickly as the film is beingproduced, and, unlike migratory cling additives, is consistent overtime, as the film is further processed & handled.

Examples 3-8

Single-sided stretch cling films of Examples 3-8 are made using the samemethods described above for the films of Examples 1 and 2. Themultilayer single-sided stretch cling films of Examples 3-8 have A/C/Bstructures as described for the films of Examples 1 and 2, except thatthe film of Example 8 use an A/C/B structure having weight ratios of 10percent/80 percent/10 percent layer thickness ratio for the respectivelayers. Table 3 sets forth the polymers utilized in the various layersof the film and the respective amounts of each polymer used. TABLE 3Example Layer A Layer B Layer C 3 99 wt % Dowlex SC2107 + Dowlex DowlexSC2107 1 wt % P-E 2 SC2107 4 97 wt % Dowlex SC2107 + Dowlex DowlexSC2107 3 wt % P-E 2 SC2107 5 95 wt % Dowlex SC2107 + Dowlex DowlexSC2107 5 wt % P-E 2 SC2107 6 93 wt % Dowlex SC2107 + Dowlex DowlexSC2107 7 wt % P-E 2 SC2107 7 91 wt % Dowlex SC2107 + Dowlex DowlexSC2107 9 wt % P-E 2 SC2107 8 91 wt % Dowlex SC2107 + Dowlex DowlexSC2107 9 wt % P-E 1 SC2107

The single-sided stretch cling films of Examples 3-8 are tested fornoise and cling levels in accordance with the procedures described abovefor Examples 1-2. The noise and cling levels and other propertiesexhibited by the films of Examples 3-8 are listed in Table 4. TABLE 4Example 3 4 5 6 7 8 Cling g- 99 106 153 160 205 96 force/inch Average μ23 23 23 23 23 23 thickness Maximum % * * * * * * Stretch MaximumKg * * * * * * Stretch Force Maximum Kg * * * * * * Unwind force Average% * * * * * * Stretch Average Kg * * * * * * Stretch Force Pre-set % 200200 200 200 200 200 stretch Sound level Db 79 79 79 79 80 79 MD Tensile9 9 9 9 9 9 Strength by ASTM D882* The values are not measured, but are expected to be the same as orsimilar to the values measured for Examples 1 and 2.

The cling level and noise generation data of Examples 3-7 are depictedgraphically in FIG. 4. FIG. 4 clearly shows that single-sided stretchcling films made in accordance with the invention exhibit relativelyhigh cling levels, while at the same time generating acceptably lownoise. Surprisingly and unexpectedly, for cling levels of between 100g-force/inch and 205 g-force/inch, the single-sided stretch cling filmsof the invention generated approximately the same amount of noise duringunwinding of the film rolls for over-wrapping operations. Additionally,Examples 3 through 8 show that films of the invention exhibit excellentcling and noise characteristics, even when very low levels of propyleneethylene copolymers are utilized.

Examples 1 and 8 demonstrate that when the propylene-ethylene copolymerutilized in the cling layer is a copolymer having 12 percent by weightunits derived from ethylene, the cling force exhibited by the film canbe significantly improved, by using a cling layer comprising 15% of thefilm structure (Example 1) versus 10% of the film structure (Example 8).Preferably, when a propylene-ethylene copolymer is used which has lessthan 15 wt % units derived from ethylene and it is desirable that thefilm exhibit at least 120 grams force per inch cling, then the clinglayer should make up at least 12 percent of the film thickness, morepreferably at least 13 percent, further more preferably at least 14percent, and most preferably at least 15 percent of the overall filmstructure thickness. Also, if it is desirable to utilize a filmstructure, wherein the cling layer makes up less than 13 percent of thefilm thickness, then a propylene-ethylene copolymer having at least 14wt % units derived from ethylene preferably is utilized, more preferablya propylene-ethylene copolymer having at least 15 wt % units derivedfrom ethylene.

Examples 9-13

Single-sided stretch cling films of Examples 9-13 are made using thesame methods described above for the films of Examples 1 and 2. Themultilayer single-sided stretch cling films of Examples 9-13 have A/C/Bstructures as described for the films of Examples 1 and 2 and weretested for cling layer to release layer cling and unwinding noise asdescribed for the films of Examples 1 and 2. Table 5 sets forth thepolymers utilized in the various layers of the film and the respectiveamounts of each polymer utilized. The cling strength values and unwindnoise levels exhibited by the films are depicted in FIG. 5. The tensilestrength and other properties listed in Table 1 were not measured forthese films, but are expected to be the same or similar to the valuesmeasured for Examples 1 and 2.

As can be seen from FIG. 5, even at low levels of propylene-ethylenecopolymer, the films exhibit excellent cling strength/unwinding noisebalance of properties. TABLE 5 Example Layer A Layer B Layer C 9 99 wt %Dowlex SC2107 + Dowlex Dowlex SC 2107 1 wt % P-E1 SC 2107 10 97 wt %Dowlex SC2107 + Dowlex Dowlex SC 2107 3 wt % P-E 1 SC 2107 11 95 wt %Dowlex SC2107 + Dowlex Dowlex SC 2107 5 wt % P-E 1 SC 2107 12 93 wt %Dowlex SC2107 + Dowlex Dowlex SC 2107 7 wt % P-E 1 SC 2107 13 91 wt %Dowlex SC2107 + Dowlex Dowlex SC 2107 9 wt % P-E 1 SC 2107

Examples 14-22

Single-sided stretch cling films of Examples 14-22 are made using thesame methods described above for the films of Examples 1 and 2. Themultilayer single-sided stretch cling films of Examples 14-22 have A/C/Bstructures as described for the films of Examples 1 and 2, except thatthe films all have an A/C/B structure having weight ratios of 10percent/80 percent/10 percent layer thickness ratio for the respectivelayers. Table 6 sets forth the polymers utilized in the various layersof the film and the respective amounts of each polymer utilized. Thecling levels exhibited by cling layer to release layer of the film isdetermined in accordance with the method described for Examples 1 and 2.The unwinding noise exhibited by the films is determined by the methoddescribed for Examples 1 and 2. The cling strength values and unwindnoise levels exhibited by the film are depicted in FIG. 6. The tensilestrength and other properties listed in Table 1 were not measured forthese films, but are expected to be the same or similar to the valuesmeasured for Examples 1 and 2.

As can be seen from FIG. 6, when the cling layer makes up less than 13percent of the film thickness, it is preferable to utilize apropylene-ethylene copolymer having greater than 14 wt % units derivedfrom ethylene, in order to increase the amount of cling exhibited by thefilm. It can also be seen from FIG. 6, that when the cling layer makesup less than 13 percent of the film thickness, it is preferable toutilize at least 5 percent by weight of the higher ethylene contentpropylene-ethylene copolymer. For thicker film structures, when thecling layer is 3 microns thick or less, it is preferable to utilize atleast 5 percent by weight of propylene-ethylene copolymer having greaterthan 14 wt % units derived from ethylene. TABLE 6 Example Layer A LayerB Layer C 14 99 wt % Dowlex SC2107 + Dowlex Dowlex SC 2107 1 wt % P-E 2SC 2107 15 97 wt % Dowlex SC2107 + Dowlex Dowlex SC 2107 3 wt % P-E 2 SC2107 16 95 wt % Dowlex SC2107 + Dowlex Dowlex SC 2107 5 wt % P-E 2 SC2107 17 93 wt % Dowlex SC2107 + Dowlex Dowlex SC 2107 7 wt % P-E 2 SC2107 18 91 wt % Dowlex SC2107 + Dowlex Dowlex SC 2107 9 wt % P-E 2 SC2107 19 99 wt % Dowlex SC2107 + Dowlex Dowlex SC 2107 1 wt % P-E1 SC2107 20 97 wt % Dowlex SC2107 + Dowlex Dowlex SC 2107 3 wt % P-E 1 SC2107 21 95 wt % Dowlex SC2107 + Dowlex Dowlex SC 2107 5 wt % P-E 1 SC2107 22 93 wt % Dowlex SC2107 + Dowlex Dowlex SC 2107 7 wt % P-E 1 SC2107

Examples 23-24

Single-sided stretch cling films of Examples 23 and 24 are made usingthe same methods described above for the films of Examples 1 and 2. Themultilayer single-sided stretch cling films of Examples 23 and 24 haveA/C/B structures as described for the films of Examples 1, except thatthe film of Example 24 has 2 percent by weight of propylene-ethylenecopolymer P-E 1 blended into the release layer B. The films were testedfor cling layer to release layer cling and unwinding noise as describedfor the films of Examples 1 and 2. The cling strength values (A-B) andunwind noise levels exhibited by the films are listed in Table 7. Thetensile strength and other properties listed in Table 1 were notmeasured for these films, but are expected to be the same or similar tothe values measured for Example 1. TABLE 7 Example (A-B) Cling,g-force/inch Sound level, db 23 108 75.2 24 175 76.6

Surprisingly, as can be seen from Table 7, a small amount ofpropylene-ethylene copolymer added to the release layer enhances thecling properties of the film, without unduly affecting the unwindingnoise generated by the film and/or the release properties or the COF ofthe release layers to one another.

1. A composition suitable for use in a cling layer of a single-sidedstretch cling film, the composition comprising: A. from 0.1 to 20% byweight of a propylene-based copolymer having substantially isotacticpropylene sequences, the propylene-based copolymer comprising propyleneand from about 10 to about 33 mole % of units derived from an alphaolefin, the propylene-based copolymer having a melt flow rate less than50 g/10 min; and B. from about 80 to about 99 % by weight of aethylene-based copolymer having a density of at least 0.905 g/cc,wherein a film made from the composition exhibits cling layer to releaselayer cling of at least 70 grams force per inch as measured by ASTMD-5458-95, noise levels of less than 87 dB during unwinding operations,and has a modulus of at least 3 MPA as determined by ASTM D-882.
 2. Thecomposition of claim 1, wherein the propylene-based copolymer exhibitsan isotactic triad tacticity level of at least 0.9, comprises from about9 to about 20 percent by weight of units derived from ethylene, has amelt flow rate of less than 25 g/10 min, and has a crystallinity of atleast 2 percent by weight and less than 40 percent by weight, andwherein the film made from the composition exhibits cling of at least100 grams force per inch.
 3. The composition of claim 1, wherein theethylene-based copolymer comprises an ethylene/1-octene copolymer havinga density of at least 0.917 g/cc.
 4. The composition of claim 2, whereinthe film exhibits cling of at least 120 grams force per inch.
 5. Thecomposition of claim 2, wherein the film exhibits cling of at least 150grams force per inch and noise levels of less than 80 dB during unwindoperations.
 6. A composition suitable for use in a cling layer of asingle-sided stretch cling film, the composition comprising: A. from 4to 12% by weight of a propylene-based copolymer having substantiallyisotactic propylene sequences, the propylene-based copolymer comprisingpropylene and from about 10 to about 17 wt % of units derived fromethylene, the propylene-based copolymer having a melt flow rate fromabout 3 to about 18 g/10 min and exhibiting a heat of fusion of lessthan about 25 Joules/gram; and B. from about 88 to about 96 % by weightof a ethylene/1-octene copolymer having a density of at least 0.917 g/ccand a melt index of from about 2 to about 12 g/10 min.
 7. Thecomposition of claim 6, wherein the propylene-based copolymer comprisesfrom about 11 to about 16 percent by weight units derived from ethylene.4
 8. The composition of claim 6, wherein the propylene-based copolymeris polymerized using an activated nonmetallocene, metal centered,heteroaryl ligand catalyst.
 9. A single-sided stretch film, the filmcomprising: A. a cling layer comprising: (1) from 0.1 to 20% by weightof a propylene-based copolymer having substantially isotactic propylenesequences, the propylene-based copolymer comprising propylene and fromabout 10 to about 33 mole % of units derived from an alpha olefin, thepropylene-based copolymer having a melt flow rate less than 50 g/10 min;and (2) from about 80 to about 99 % by weight of a ethylene-basedcopolymer having a density of at least 0.905 g/cc; and B. a releaselayer comprising a polyethylene having a density of at least 0.905 g/cc,wherein the film exhibits a cling layer to release layer cling of atleast 70 grams force per inch as measured by ASTM D-5458-95, noiselevels of less than 87 dB during unwinding operations, and has a modulusof at least 3 MPA as determined by ASTM D
 882. 10. The single-sidedstretch cling film of claim 9, wherein the release layer (B) comprises apolyethylene having a density of at least 0.917 g/cc.
 11. Thesingle-sided stretch cling film of claim 9, wherein the film exhibits acling of at least 100 grams force per inch, a noise level of less than80 dB, and has a modulus of at least 6 MPa.
 12. The single-sided stretchcling film of claim 11, wherein the cling layer (A) comprises from 4 to12 percent by weight of a propylene-ethylene copolymer having from 10 to17 percent by weight units derived from ethylene and a melt flow rate ofless than 25 g/10 min.
 13. The single-sided stretch cling film of claim12, wherein the film exhibits a cling of at least 150 grams force perinch, and has a modulus of at least 7 MPa.
 14. The single-sided stretchcling film of claim 13, wherein the ethylene-based copolymer of thecling layer comprises an ethylene/1-octene copolymer.
 15. Thesingle-sided stretch cling film of claim 14, wherein theethylene/1-octene copolymer has a density of at least about 0.917 g/cc.16. The single-sided stretch cling film of claim 15, wherein theethylene/1-octene copolymer has a melt index of from about 2 to about 12g/10 min.
 17. The single-sided stretch cling film of claim 9, whereinthe release layer further comprises from 0.1 to 2 percent by weight of apropylene-based copolymer.
 18. The single-sided stretch cling film ofclaim 17, wherein the propylene-based copolymer comprises apropylene-ethylene copolymer.
 19. The single-sided stretch cling film ofclaim 17, wherein the coefficient of friction of the release layer toitself is less than 1.0.
 20. The single-sided stretch cling film ofclaim 19, wherein the coefficient of friction of the release layer toitself is from 0.15 to 0.7.
 21. The single-sided stretch cling film ofclaim 17, wherein the cling of the release layer to itself is less than60 grams-force/inch.